The long term goal of this research is to develop a fiberoptic-based reflectance instrument to noninvasively measure oxygen in circulatory and intracellular tissue compartments. Phase I successfully demonstrated the feasibility of employing curve fitting spectral analysis to simultaneously measure epicardial dissolved oxygen and the oxygenated and deoxygenated forms of myoglobin and hemoglobin in epicardial tissue. This methodology will be applied during Phase II to the development of an instrument with increased sensitivity to resolve hemoglobin, myoglobin and mitochondrial cytochromes. The commercial utility of the device will be demonstrated through its application to studies of working mammalian hearts and studies of ischemia in skeletal muscle. The tasks to be undertaken during Phase II will be to: . determine optimal reflectance standards for curve fitting reflectance spectra from epicardium and skeletal muscle . construct an optical fiber-coupled imaging spectrograph to monitor tissue oxygen at two different tissue regions simultaneously . evaluate the Tissue Oxygen Monitor's potential by simultaneously monitoring oxygenation of epicardium and endocardium in working perfused mammalian heart . further demonstrate the instrument's utility through its employment in a magnetic resonance study of skeletal muscle ischemia